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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - jsc-tailcall: JavaScript functions should restore the stack pointer after a call"
href="https://bugs.webkit.org/show_bug.cgi?id=146846#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - jsc-tailcall: JavaScript functions should restore the stack pointer after a call"
href="https://bugs.webkit.org/show_bug.cgi?id=146846">bug 146846</a>
from <span class="vcard"><a class="email" href="mailto:basile_clement@apple.com" title="Basile Clement <basile_clement@apple.com>"> <span class="fn">Basile Clement</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=146846#c1">comment #1</a>)
<span class="quote">> Created <span class=""><a href="attachment.cgi?id=256709&action=diff" name="attach_256709" title="Patch using StackMap size">attachment 256709</a> <a href="attachment.cgi?id=256709&action=edit" title="Patch using StackMap size">[details]</a></span>
> Patch using StackMap size
>
> This uses the stackmap size from LLVM to restore the stack pointer to where
> it should be in the patchpoint. I am interested in hearing opinions on the
> following two points:
>
> - We may want to adapt the default patchpoint size to accommodate the
> additional lea opcode.
>
> - LLVM provides a stackmap/stackrestore intrinsic that we should be able to
> use. I am unsure what guarantees we would have with this; in particular, I
> fear LLVM spilling values onto the stack before the call but after saving
> the stack pointer, performing the call, then trying to restore those values
> using the stack pointer as it is supposed to be callee-save. I did not see
> this happen even when testing that approach with high register pressure
> (LLVM ends up using bp-based offsets for the spilling), but again, I am
> unsure how much we can rely on this. I believe messing up with the stack
> pointer in the patchpoint is better because it makes it completely
> transparent to LLVM.</span >
After talking offline with fpizlo, the stackmap size approach looks like the best one.</pre>
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